The present invention relates to a cardioversion/defibrillation electrode and more particularly to a patch electrode having an improved structure to simplify implantation procedures and to preserve the structural integrity of the electrode after implantation.
In the field of cardioversion/defibrillation, electrodes are mounted in, on or about the heart to discharge and generate an electric field which is capable of terminating potentially lethal tachyarrhythmias. The electrodes come in various forms, including endocardial catheter electrodes, epicardial patch electrodes, and subcutaneous electrodes. A conventional patch electrode such as shown in U.S. Pat. No. 4,291,707--Heilman et al is designed to attach on or near the heart surface and is generally a thin planar device having a lead extending therefrom which connects electrically conductive surfaces on the electrode with a source of electrical energy, typically embodied as an implantable pulse generator.
The patch electrode includes conductive surfaces on the side designed to face the heart. These conductive surfaces may take on a variety of shapes and sizes. One type of conductive element useful on a patch electrode is a conductive mesh. The conductive mesh is attached to an insulative backing material and is connected to insulated electrically conductive leads. To adapt to the changing surfaces of the heart during cardiac contractions and to facilitate implantation into the thoracic region, some patch electrodes have been designed with a degree of flexibility.
A problem with patch electrodes heretofore known is that during intrathoracic introduction procedures, the electrode must be bent and contorted to achieve proper placement on or about the heart. Consequently, the conductive mesh on the electrode is subject to a bending stress which may exceed the mesh material yield stress, with the result that it may become permanently deformed after the introduction procedure. The permanently deformed electrode may not function properly since the conductive mesh no longer conforms optimally to the generally curved surfaces of the epicardium.
U.S. Pat. No. 5,042,463--Lekholm et al discloses several embodiments of a flexible, planar patch electrode for defibrillation in which there are "conductor-free" zones in which the patch could be folded without deforming the electrode conductor. However, in these "conductor-free" zones the insulative backing is removed, such that the electrode would not have a resilient spring-like hinge effect that would aid in returning the planar patch to its natural planar state during deployment. Thus, any folding of the planar patch electrode shown in the Lekholm et al patent during an implantation procedure would cause irreparable deformation and possible damage of the electrode conductor in the region of the electrode where the lead portion joins the electrode portion. U.S. Pat. No. 4,827,932--Ideker et al illustrates a large partially bifurcated conformal mesh patch for epicardial defibrillation. However, it teaches contiguous mesh conductive surfaces without regard for the prevention of deformation of the mesh conductive surface. U.S. Pat. No. 4,938,231 Milijasevic depicts an electrode having "conductor-free" zones, but they are in the form of radial slits and semi-circular slots that would prevent folding for improved deployment using minimally invasive techniques.